Bonded weather resistant decorative laminate with slightly grained acrylic surface

ABSTRACT

1. A UNITARY, HEAT AND PRESSURE BONDED WEATHER RESISTAND DECORATIVE LAMINATED ARTICLE COMPRISING: (A) A RIGIDITY IMPARTING CORE LAYER COMPRISING A PLURALITY OF SHEETS IMPREGNATED WITH PHENOLIC RESIN, (B) A PRINT SHEET LAYER IMPREGNATED WITH AMINOTRIAZINE-ALDEHYDE RESIN BONDED TO THE CORE LAYER, AND (C) A TOP METHYL METHACRYLATE PROTECTIVE SHEET LAYER CONSISTING ESSENTIALLY OF METHYL METHACRYLATE HOMOPOLYMERS HAVING AVERAGE MOLECULAR WEIGHTS FROM ABOUT 320,000 TO 550,000, SAID PROTECTIVE SHEET BEING A PRE-FORMED FILM HAVING A SLIGHTLY GRAINED SURFACE BEFORE BONDING, SAID SLIGHTLY GRAINED SURFACE BEING DIRECTLY BONDED TO SAID PRINT SHEET LAYER WITHOUT THE USE OF A SEPARATE ADHESIVE LAYER, THE SLIGHTLY GRAINED SURFACE BEING EFFECTIVE TO PERMIT GAS BLEED OFF BETWEEN THE PRINT SHEET AND THE PROTECTIVE SHEET DURING BONDING OF THE ARTICLE.

Oct. 15, 1914 5 PALAZZOLQ ETAL 3,841,956

BONDED WEATHER RESISTANT'DECORATIVE LAMINATE WITH SLIGHTLY GRAINEDACRYLIC SURFACE Filed Oct. 24. 1972 .FIG.I

United States Patent Oflice 3,841,956 Patented Oct. 1974 U.S. Cl.161-248 9 Claims ABSTRACT OF THE DISCLOSURE A weatherproof outdoorlaminate is made from a core layer impregnated with a phenolic resin, aprint sheet layer impregnated with an aminotriazine-aldehyde resin andan outer protective layer of methyl methacrylate consisting of polymershaving a molecular weight from about 320,000 to 550,000, wherein theouter layer has a surface effective to allow gas bleedability that isbonded directly to the print sheet layer without the use of a separateadhesive layer.

CROSS REFERENCE TO RELATED APPLICATIONS This application is acontinuation-in-part application of application U.S. Ser. No. 94,848,now abandoned filed on Dec. 3, 1970.

BACKGROUND OF THE INVENTION This invention relates to low cost,weatherproof, outdoor decorative laminates. More particularly, thisinvention relates to outdoor laminates of a phenolic impregnated corelayer protected by an outer poly (methyl methacrylate) layer consistingof high molecular weight polymers, which is bonded directly to the bodyof the laminate without the use of a separate adhesive layer.

Acrylic films were marketed in 1967. These films exhibited highresistance to the efiects of ultraviolet radia tion, good retention offlexibility of exterior aging, and outstanding resistance to yellowingunder both heat and light exposure. The film was suggested for presslamination without adhesive to wood veneer, paper and plasticsubstrates.

The advantages of laminate protective overlay sheets of homopolymers andmodified copolymers of methyl methacrylate, having low molecular weight,was also recognized by Pounds in U.S. Pat. No. 3,345,248 and Petropoulosin U.S. Pat. No. 3,220,916. Pounds and Petropoulos taught replacing anaminotriazine-aldehyde sheet, as a protective overlay for amelamine-formaldehyde resin impregnated decorative sheet in an outdoorlaminate, with a sheet of methyl methacrylate consisting of polymershaving an average molecular weight (IWI from about 60,000 to 250,000.

Pounds and Petropoulos taught however that preformed film sheets ofmethyl methacrylate consisting of polymers having average molecularweight (M over 250,000 could not be bonded to the melamine-formaldehyderesin impregnated decorative sheet of laminates having phenolic resinimpregnated core members, without using temperatures and pressuresharmful to the laminate. Such laminate protective sheets of highermolecular weight polymers would however be advantageous, and extremelyuseful, due to greater resistance to chemical and other environmentalattack, particularly solvent resistance, and the use of pre-formed filmsheets would allow commercial manufacture of this type outdoor laminate.

There is a need, therefore, for new and improved acrylic protectivecoatings for laminates. This need encompasses a need for new methods offabricating acrylic protective coated laminates having thinner and lessexpensive protective coatings of high molecular weight polymers.

SUMMARY OF THE INVENTION We have found the poly (methyl methacrylate)sheet, comprising polymers having an average molecular weight (M ofbetween about 320,000 and 550,000 and having a gas bleed off surfacefinish, can be laminated, without auxiliary adhesive, to a decorativesheet of paper impregnated with a melamine-formaldehyde resin supportedby a plurality of phenolic resin impregnated core sheets. The final bondis developed under the influence of about 1200 psi. and 290 F. in apress. The product has strong bond adhesion which resists weakening ordelamination under testing and is useful as a superior outdoor laminate.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of theinvention, reference may be made to the preferred embodiments, exemplaryof the invention, shown in the accompanying drawings in which:

FIG. 1 .shows an exploded three dimensional view of one embodiment ofthe laminate of this invention; and

FIG. 2 shows a cross section of the laminate in consolidated form.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The protective outer layer usedin this invention is based on poly (methyl methacrylate) sheet preparedfrom polymers having average molecular weights (H substantially above250,000. This film is commercially available under the tradename Korad Cin thicknesses from 2 to 6 mils.

Acrylic plastics are made by free radical catalysts acting on monomericmethyl methacrylate. They are rigid thermoplastics made from upwards ofpercent methyl methacrylate, the remainder being an ester of acrylic ormethacrylic acid. Most molding compositions are copolymers of methylmethacrylate with 1 to 12 percent of ethyl acrylate as a modifier toprovide increased flow in moldmg.

The all-acrylic resins range from soft gums such as polymers of ethylacrylate or octyl methacrylate through flexible materials such aspolybutyl methacrylate to rigid polymethyl methacrylate. Byco-polymerization of various acrylic monomers, an essentially continuousrange of softness and solubility is obtainable.

Casting and extrusion are the two basic methods of producing acrylicsheet. In extrusion, the sheet is produced from solid acrylic polymersby a melt process through a die. In casting, the sheet is produced fromcatalyzed monomer or a syrup of partially polymerized monomer which maybe poured into cells made from two sheets of glass with a compressiblegasket around the edge. The stock is cured in ovens or a water bath,usually followed by further heating at about 220 F. to complete thepolymerization and eliminate shrinkage strains. To increase melt flow inthermoforming, up to about 10 percent by weight of a plasticizer such asdioctyl phthalate, dibutyl phthalate, polyethylene glycols or alkylacrylates such as ethyl acrylate may be incorporated in the monomer. Theacrylic sheet may also be continuously cast where the chemical reactionof the blend of monomer and catalyst is controlled to result in rapidcure.

The acrylic plastic sheet used in this invention consists of highmolecular weight methyl methacrylate homopolymers with a small amount oflow molecular weight plasticizer. Its number average molecular weight (Mis approximately 308,000 and its weight average molecular weight (M isapproximately 654,000 with a polydispersity ratio (M /M of 2.13. Theaverage molecular weight of the nonmodified poly (methyl methacrylate)plastic sheet used in this invention based on intrinsic vis costiymeasurements (M is between the M and lil values of 308,000 and 654,000and more specifically between about 320,000 and 550,000.

The flexible thin-gauge pre-formed acrylic plastic sheet used in thisinvention ranges in thickness from about 1 to mils and has a mat orslightly grained, roughened surface finish before bonding on at leastone side. This nonsmooth finish can permit air to bleed oil between thesheet and the polished press plate and more importantly between thesheet and the substrate during lamination. While it is necessary to havethe gas bleedable finish contacting the laminate assembly it is notnecessary to have it contacting the press plate. It is believed that thenonsmooth finish substantially contributes to bondability Withoutdestruction of the laminate. It is believed that the nonsmooth finishalso allows gaseous steam condensation products of phenol or melamineformaldehyde to bleed oif between the sheet and the substrate duringlamination. Such surfaces, effective to permit gas bleed ofi duringbonding, whether grained, roughened, scored or embossed, would appear tobecome more important as larger commercial type laminate sizes, i.e.above about 2' x 2' are approached, due to the long gas diffusion escapepath from the center of the sheet to the edge during bonding.

Referring now to FIG. 1, the pre-formed high molecular weight poly(methyl methacrylate) protective sheet 1 used in this invention is shownwith gas bleedable surfaces 2 and 3 on each side of the sheet. Thesesurfaces are shown as grained but may be cross hatched, ribbed, or treadscribed, in order to allow gas bleed off during bonding to the assembly.

The print sheet layer shown as a 4 in the drawings is disposed betweenthe core and protective layer and usually provides the decorative eifectfor the laminate. It is usually in the form of a decorative sheet, i.e.dyed, pigmented to impart a solid color, or printed with an ornamentaldesign such as wood or marble grain. It usually comprises a single sheetof high grade absorbent alphacellulose or regenerated cellulose paperimpregnated with a substantially cured, fusible or B-staged,aminotriazinealdehyde resin, usually a thermosettablemelamine-formaldehyde resin. Other useful print sheet materials arekraft paper, synthetic fiber paper, cotton, linen and glass fiberfabrics and the like.

The rigidity-imparting core layer 5 usually comprises a plurality ofsheet of kraft paper impregnated with phenolic resin.

Melamine is the preferred aminotriazine reactant for preparing theaminotriazine-alehyde resin used to impregnate the print sheet. Melamine(1,2,5 triamino-2,6,6-triazine or cyanouramine) can be prepared byheating urea in the presence of ammonia at temperatures of 250 to 350 C.

Melamine can also be produced from dicyandiamide which is obtained bypolymerization of cyanamide at elevated temperatures. The melamine isreacted with an aldehyde such as formaldehyde to yield a potentiallythermoset resinous condensate capable of being converted under heat andpressure to a substantially insoluble and infusible form (see US. Pat.2,197,357 and Brydson, Plastics Materials, D. Van Nostrand, 1966Melamine- Formaldehyde Resins, pp. 418-427).

The mol ratio of aldehyde to aminotriazine in the resinous reactionproduct may be within the order of from about 1:1 to about 6:1respectively. Conventional reaction conditions are observed in preparingthe resin. Formaldehyde and water are charged and the pH adjusted to7.5-9 with sodium hydroxide solution. The melamine is then added and thebatch heated to reflux at about 210 F. and about 8-10 p.s.i. steampressure. If desired, the thermosetting aminotriazine-aldehyde resin maybe modified by the addition of plasticizers or curing catalysts. Otheraminotriazines, e.g. mono-, diand tri-methylmelamines, and the like;guanamines, such as formoguanamine, acetoguanamine, benzoguanamine, andthe like, as Well as mixtures of aminotriazines, may also be utilized asreactants. Similarly, formaldehyde, either as such or as an aqueoussolution, is the preferred aldehyde reactant, but other aldehydes, e.g.acetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, dialdehydesand the like, or compounds engendering aldehydes, e.g.,paraformaldehyde, hexamethylene-tetramine, and the like, may also beemployed. Such aminotriazine-aldehyde resins are well known in the artand reference may be made to US. Patent 3,392,082 for exhaustive detailson their production.

The thermosetting phenolic resins used to impregnate the plurality ofcore sheets are Well known in the art (see US. Pats. 2,205,427;2,315,087; 2,328,592 and 2,383,430 and Brydson Plastic Materials, D. VanNostrand, 1966, Chapter 19). They are conventionally obtained byreacting a phenolic substance such as phenol itself, substitutedphenols, e.g., alkyl phenols such as cresols, xylenols, tertiary alkylphenols, and the like, or mixtures of such phenolic substances with analdehyde such as formaldehyde, acetaldehyde, propionaldehyde,benzaldehyde, furtural, and the like, or with mixture of such aldehydes,either alone or in the presence of other aldehyde-reactable substancessuch as urea, thiourea, substituted ureas and thioureas, aminotriazines,e.g., melamine, lignin derivatives, and the like.

The print sheet and core sheets are impregnated using standardtechniques. The print sheet will be impregnated with a solution ofaminotriaZine-aldehyde resin to give a resin content between 30% and byweight, based on the total dry weight of the impregnated sheet and thendried to a stage where the volatile content is between 2% and 10%. Thecore layer sheets are impregnated with a solution of phenolic resin togive a resin content between 25% and 40% by weight, based on the totaldry weight of the impregnated sheet, and then dried to a stage at whichthe resin is only partly cured and has a volatile content between 4% and15%.

High pressure laminating techniques are employed in preparing laminatesfrom the above described core layer of core sheets, print sheet layerand top high molecular weight poly (methyl methacrylate) sheet layer.The print sheet layer will generally be a decorative sheet and may carrya pattern. The high molecular weight poly (methyl methacrylate) layermay be transparent or pigmented. In the latter case a subsurface sheetwould not be required, the top methacrylate sheet being bonded directlyto the corestock without an adhesive.

The high molecular weight poly (methyl methacrylate) top layer is placedagainst the print sheet layer. No adhesive cement layer is used to bondthe two together. Then the top layer and print sheet layer are assembledwith the rigidity-imparting core sheets, and inserted in a laminatingpress between press plates which are generally stainless steel and mayhave finishes ranging from a mirror polish to a mat surface. Theassembly is then consolidated by means of heat and pressure into aunitary decorative structure.

Temperatures ranging from about 250 F. to about 320 F. and pressuresranging from about 1000 p.s.i. to 1500 p.s.i. are employed. The totaltime required to effect a cure of the resinous components of theassembly will usually be from about 5 minutes to about 45 minutes at thecuring temperature. The resulting laminate is generally allowed to coolto about F. before being removed from the press. In certain cases it maybe desirable to use a thin release sheet, such as for example a sheet ofmetal foil or paper coated with a release agent such as calciumstearate, or other means such as a coating of calcium stearate betweenthe protective layer and the press plate of the laminating mold toproduce special surface texturing elfects.

The invention is illustrated by the following example.

Example I A roll of 105 lb. kraft paper was treated a solution ofphenol-formaldehyde resin to give a resin content between 31% and 35%and then dried to a stage at which the resin was only partly cured andhad a volatile content between 6% and 9%. Equal size impregnated coresheets, 12" x 18", were cut from the roll and assembled in a stack of 7sheets to form a core layer. A white plgmented phenol-formaldehydeimpregnated core sheet was placed on the stack to provide a subsurfacesheet A layer comprising a 12" x 18" print sheet of white pigmentedalpha-cellulose paper was impregnated with melamineformaldehyde resinand superimposed on the subsurface sheet followed by a 12" x 18" clear,pro-formed high molecular weight poly (methyl methacrylate) film sheet2.0 mil thick, having a mat or slightly grained, roughened surfacefinish on both sides. The acrylic sheet had a molecular weight (Mbetween about 320,000-550,000, a specific gravity (ASTM D-79264T basedon H O at 23 C.) of 1.17, a water absorption rate (ASTM D-570-63 basedon 24 hrs. at 23 C.) of 0.7 percent and a water vapor transmission rate(ASTM E-96-63T) of gr./24 hrs./ 100 in. under the tradename Korad C.

The melamine-formaldehyde resin content of the print sheet prior todrying was between 41% and 43% and after curing it had a volatilecontent between 3.5% and 5.0%. No adhesive cement layer was used betweenthe high molecular weight poly (methyl methacrylate) protective film andthe print sheet surface.

The assembly was placed in a press and molded against a chrome polishedsteel pressing plate at 1200 p.s.i. with a platen temperature of 315 F.The controlled internal temperature was 4 minutes above 270 F. with amaximum temperature of 290 F. The assembly was heated in the press for atotal of about 30 minutes. About 20 minutes was required for warm-upafter placing the laminate in the press.

The laminate was allowed to cool for about 5 minutes and then thedurability of the high molecular weight poly (methyl methacrylate) bondto the laminate substrate was tested by the National ElectricalManufacturers Association (NEMA Test ID1-2.'07), Test for Immersion inBoiling Water. After two hours boiling by this test, the specimen wasexamined for evidence of delamination. The boiled specimen showed nosign of "a weakened bond, either in the wet condition or after dryingout.

The laminate was also tested in an Atlas Weather- Ometer according toASTM standards 1342-65 and D1499-64. This device rotates the sample sothat it is successively exposed to ultraviolet light from a carbon arcand to a spray of distilled water. The carbons are changed after 19-20hours so that the sample is normally aged about 100 hours per week. R.J. Martinovich and G. R. Hill in a paper presented at the Symposium onthe Weatherability of Plastic Materials, Feb. 8 and 9, 1967 at theNational Bureau of Standards, Gaithersburg, Maryland, stated thatWeather-0meter results indicated that 1000-2000 hours exposure isapproximately equivalent to 12-24 months in Arizona at 45 South. Theyalso stated that one year exposure in Arizona is roughly equivalent to 2years in Oklahoma and 3 years in Ohio. Our tests show that the specimenhad no serious imperfections, color change, chalking or delaminatedareas in the laminate after 2000 hours exposure in the Weather-Ometer.

The melamine formaldehyde impregnating resins were prepared as follows.

To 1620 lbs. (20 moles) of 37% formaldehyde, with a pH adjusted to about7.5 with sodium hydroxide, was added 1260 lbs. (10 moles) ofrecrystallized melamine. The slurry pH was adjusted to about 8.2 with10% sodium hydroxide as needed. The mixture was heated to reflux (98-99C.) and held at that temperature until a drop or two of the batch whendropped into water at 25 C formed a cloudy tail as the droplet dispersedthroughout the water. At this point the.reaction temperature was reducedto about C. and then cooled to 60-65 C. and the following materialsadded in order, 200 lb. of ethyl alcohol, o,p-toluene sulfonamide and186 lbs. of methyl glucoside. Mixing was continued to complete solution.Finally 734 lbs. of water were added and the pH adjusted to about 9.1 toproduce a composition suitable for saturating the print paper.

To 940 lbs. (10 moles) of molten phenol were added 1012 lbs. (12.5moles) of 37% formaldehyde solution. To this was added a sodiumhydroxide solution containing 15 lbs. (0.375 moles) of sodium hydroxideflakes dissolved in 30 lbs. of water. The mixture was reacted at 98 C.reflux and then diluted with methyl alcohol to a solids content of about41% determined by a standard procedure of heating the specimen of resinfor two hours at C. This varnish was used to saturated kraft paper forthe core stack of the laminate.

We claim:

1. A unitary, heat and pressure bonded weather resistant decorativelaminated article comprising:

(a) a rigidity imparting core layer comprising a plurality of sheetsimpregnated with phenolic resin,

(b) a print sheet layer impregnated with aminotriazine-aldehyde resinbonded to the core layer, and

(c) a top methyl methacrylate protective sheet layer consistingessentially of methyl methacrylate homopolymers having average molecularweights from about 320,000 to 550,000, said protective sheet being apre-formed film having a slightly grained surface before bonding, saidslightly grained surface being directly bonded to said print sheet layerwithout the use of a separate adhesive layer, the slightly grainedsurface being effective to permit gas bleed ofl between the print'sheetand the protective sheet during bonding of the article.

2. The article of claim 1 wherein the phenolic resin is aphenol-formaldehyde resin, the aminotriazine-aldehyde resin is amelamine-formaldehyde resin and the protective layer has a slightlygrained surface on both sides.

3. A unitary, heat and pressure bonded weather resistant decorativelaminated article comprising:

(a) a rigidity imparting core layer comprising a plurality of sheetsimpregnated with phenol-formaldehyde resin,

(b) a print sheet layer impregnated with melamineformaldehyde resinbonded to the core layer,

(0) a top methyl methacrylate protective sheet layer consistingessentially of methyl methacrylate homopolymers having average molecularweights from about 320,000 to 550,000, said protective sheet being apre-formed film about 1 to 10 mils thick, said protective sheet having aslightly grained surface before bonding effective to permit gas bleedoff between the print sheet and the protective sheet during bonding ofthe article at about. 250-320 F. and 1000-1500 p.s.i., said gasbleedable surface being directly bonded to said print sheet layerwithout the use of a separate adhesive layer.

4. The article of claim 3 wherein the protective layer has a gasbleedable surface on both sides.

5. The article of claim 3 wherein the protective layer contains up toabout 10 percent by weight plasticizer.

6. The article of claim 5 wherein the protective layer consistsessentially of plasticizer and non-modified methyl methacrylatehomopolymers, the article is larger than about 2 ft. long 2 ft. wide,and the sheets of the core layer and the print sheet layer are papersheets.

7. A method for producing a unitary, heat and pressure consolidatedweather resistant decorative laminated article comprising the steps:

(a) preparing an assembly, in superimposed relationship of:

(i) a plurality of thermosetting phenolformaldehyde resin impregnatedcore sheets,

7 (ii) 1 a melamine-formaldehyde resin impregnated print sheet, (iii) atop methyl methacrylate protective sheet consisting essentially ofmethyl methacrylate homopolymers having molecular weights from about320,000 to 550,000, said protective sheet being a pre-formed film about1 to 10 mils thick having a surface efiective to permit gas bleed offduring bonding, said gas bleed'able surafce contacting the print sheetwithout a separate adhesive layer therebetween, and (b) heat andpressure consolidating the assembly, be-

tween about 250-320 F. and 10001500 p.s.i., to a unitary structure. 8.The method of claim 7 wherein the protective layer has a slightlygrained surface on both sides.

, i 9. The method of claim 7 wherein the article is above about 2 ft.long x 2 ft. Wide.

References Cited UNITED STATES PATENTS GEORGE F. LESMES, PrimaryExaminer PATRICIA C. IVES, Assistant Examiner US. Cl. X.R.

1. A UNITARY, HEAT AND PRESSURE BONDED WEATHER RESISTAND DECORATIVELAMINATED ARTICLE COMPRISING: (A) A RIGIDITY IMPARTING CORE LAYERCOMPRISING A PLURALITY OF SHEETS IMPREGNATED WITH PHENOLIC RESIN, (B) APRINT SHEET LAYER IMPREGNATED WITH AMINOTRIAZINE-ALDEHYDE RESIN BONDEDTO THE CORE LAYER, AND (C) A TOP METHYL METHACRYLATE PROTECTIVE SHEETLAYER CONSISTING ESSENTIALLY OF METHYL METHACRYLATE HOMOPOLYMERS HAVINGAVERAGE MOLECULAR WEIGHTS FROM ABOUT 320,000 TO 550,000, SAID PROTECTIVESHEET BEING A PRE-FORMED FILM HAVING A SLIGHTLY GRAINED SURFACE BEFOREBONDING, SAID SLIGHTLY GRAINED SURFACE BEING DIRECTLY BONDED TO SAIDPRINT SHEET LAYER WITHOUT THE USE OF A SEPARATE ADHESIVE LAYER, THESLIGHTLY GRAINED SURFACE BEING EFFECTIVE TO PERMIT GAS BLEED OFF BETWEENTHE PRINT SHEET AND THE PROTECTIVE SHEET DURING BONDING OF THE ARTICLE.